Integrated circuit devices are widely used for consumer, commercial and other applications. As is well known to those having skill in the art, integrated circuit devices typically include a large number of active devices such as transistors in a microelectronic substrate, such as a semiconductor substrate. The devices are interconnected in a desired interconnection pattern using one or more levels of patterned conductor layers, often referred to as “metallization”. As the integration density of integrated circuit devices continues to increase, copper-based metallization schemes have been developed to allow improved interconnect performance.
Copper interconnections are often formed using a damascene and/or dual damascene process, wherein trenches and/or vias are formed in one or more dielectric layers, overfilled with copper and then polished to remove the excess copper outside the trenches. Conventionally, a copper-based metallization is formed in a trench on an integrated circuit substrate by forming a liner that comprises refractory metal in the trench, forming a copper plating seed layer on the liner, and then plating copper on the copper plating seed layer. The refractory metal may be tantalum, although other refractory metals such as titanium and tungsten also may be used.
Conventionally, the liner includes a refractory metal nitride layer, such as a tantalum nitride layer, and a refractory metal layer, such as a tantalum layer, on the refractory metal nitride layer. The liner and the copper plating seed layer may be fabricated using physical vapor deposition and/or chemical vapor deposition.
As is well known to those having skill in the art, vapor deposition refers to processes in which materials in a vapor state are condensed through condensation, chemical reaction and/or conversion, to form a solid material. Vapor deposition processes may be classified into physical vapor deposition and chemical vapor deposition.
In physical vapor deposition, a thin film of material is deposited on a substrate by converting the material into vapor by physical means, transporting the vapor across a region of low pressure from its source to the substrate, and causing the vapor to undergo condensation on the substrate to form the thin film. Sputtering is a widely used physical vapor deposition method for integrated circuit fabrication. In sputtering, atoms are dislodged from the surface of a material as a result of collision with high energy particles. The atoms or molecules that are ejected from the target material condense on the substrate as a thin film.
In contrast, chemical vapor deposition refers to formation of a solid film on a substrate from a reaction of vapor phase chemical reactants containing the desired constituents. A reaction chamber is used for this process, into which reactive gases are introduced, to decompose and react with the substrate to form a film. Thus, in chemical vapor deposition, a predefined mix of reactant gases and diluent inert gases are introduced at a specified flow rate into a reaction chamber. The gas species move to the substrate, and the reactants are adsorbed to the surface of the substrate. The reactants undergo chemical reactions with the substrate to form the film. Atomic layer deposition is one form of chemical vapor deposition in which a film is deposited one atomic or molecular layer at a time.
In forming a liner with tantalum and/or tantalum nitride, it is known that these materials may be oxidized by adsorbed water during processing, according to the following chemical reactions:

This oxidation can degrade the adhesion between the liner and the subsequently formed copper layers, which can degrade the reliability of the interconnects by creating voids, as described, for example, in Yatsuta et al., Quantitative Control of Plasma-Surface Interactions for Highly Reliable Interconnects, Proceedings of the IEEE 2004 International Interconnect Technology Conference, Jun. 7-9, 2004, pp. 90-92. These voids may cause electromigration problems in the interconnect.
It is also known that enough hydrogen partial pressure can reduce or suppress the reaction between Ta/TaN and water, as shown by the following reactions:

Accordingly, it is known to perform a hydrogen-containing plasma treatment on a copper-based metallization system, by exposing the plated copper layer to a hydrogen plasma treatment, before depositing a subsequent dielectric layer. This hydrogen pretreatment may be performed at 350° C. after chemical mechanical polishing is performed on the integrated circuit substrate to remove the plated copper, the copper seed layer and/or the liner layer outside the trench, but prior to forming a subsequent dielectric layer on the copper-filled trenches.
It has been found that the hydrogen pretreatment of the copper layers in the trenches can provide electromigration lifetime improvements of up to 5 to 10 times or more. Unfortunately, however, this increase in electromigration lifetime may be accompanied by an undesirable increase in leakage current and/or line resistance of the copper metallization.